1. Field of the Invention
The present invention relates generally to drilling and completion fluid recovery and, more specifically, to a system for preventing wellbore fluids from being spilled when the threaded connections between the joints of the wellbore tubulars are disconnected, while being tripped out of the wellbore.
2. Description of the Background
During what is sometimes called a xe2x80x9cwetxe2x80x9d trip, a release of drilling fluid may occur with each of a large number of drill pipe connections that are broken. As the drill pipe string is being removed from the well, for example to substitute a new drilling bit for a worn drilling bit, the drilling mud that may remain in the string can create considerable problems. Each stand of drill pipe may be approximately ninety feet long in accordance with the drilling rig size. Depending on well conditions, the pipe which is removed may therefore contain up to a ninety-foot column of drilling fluid therein. Although variable based on the size of the drill pipe, the volume of fluid in a ninety-foot column may be in the range of as much as one hundred fifty gallons. When a threaded joint between the stand of drill pipe and the drill string is disconnected, this column of mud is released to flow from the length of the drill pipe. This release of wellbore fluids may typically occur m any times during a xe2x80x9cwetxe2x80x9dtrip.
Drilling and completion fluids which include fluids such as weighted mud, oil-based fluids, water-based muds and the like are often quite expensive and may frequently cost more than one million dollars per well. Loss of such fluids during the numerous pipe trips made per well can therefore be quite costly as the fluids will need to be replaced. Moreover, the loss of such fluids can also create pollution which is highly undesirable. As well, the fluids may create an unusually slippery rig floor and surroundings so as to cause safety problems by increasing the likelihood of accidents to operators working on the rig floor.
The above problems are well known in the oil industry and therefore many efforts have been made in past years to limit spillage. One exemplary prior art system for a drilling mud container apparatus is disclosed in U.S. Pat. No. 5,295,536, issued Mar. 22, 1994, to Robert E. Bode, and is incorporated herein by reference. The drilling mud container apparatus provides a container for preventing spilling of drilling mud onto the rig floor to thereby save the mud for later reuse. The invention includes a diametrically split and hinged barrel having a fixed lower seal assembly and a movable upper seal assembly which engage the outer wall of the drill pipe respectively below and above a joint connection that is to be unthreaded. Upon disconnection of the joint and upward movement of the drill pipe, the upper seal moves upward with the pipe to eliminate wear which otherwise would result in seal and mud leakage. The container includes a large drain port and is adapted to be connected to a suitable hose which leads to a mud pit or tank.
However, several significant problems still exist with prior art fluid recovery systems. One problem relates to the amount of time required for the recovery system to operate. Draining large amounts of fluid as each connection is broken considerably increases the overall effective time required to break each connection and therefore significantly increases the time required for tripping the drilling string out of the wellbore. Therefore, the associated time costs of wet trips may also significantly increase the cost of drilling the well. As another factor, unless considerable time is allowed for drainage and dripping, depending on the viscosities and flow rates of the fluid, size and length of pipes, drilling fluid losses may still occur that are greater than permissible under governmental regulations even though the losses are greatly reduced. Another problem is related to the size of the container that must be secured around the pipe joint. To avoid the need for numerous different size containers related to the expected volume of fluid and size of pipe, a single container size with removable seals designed for each pipe size is generally constructed to be large enough in volume to handle the largest flows anticipated. However, due to this large size, the container can be awkward to work with thereby resulting in more loss of time as well as the inconvenience and hazards of working with unwieldy and bulky equipment.
Consequently, it would be desirable to further improve prior art drilling and completion fluid recovery prior art systems. It would be highly desirable to reduce loss of drilling fluid even more than has been possible in the past, and to do so in much less time. It would also be desirable to reduce the size of the container used in prior art systems while still retaining the ability to handle the maximum possible fluid flow as the pipe connection is broken. Thus, it would be desirable to save the considerable cost due to time loss while even further reducing any loss of expensive and possibly environmentally harmful drilling fluids. It is always desirable to further improve safety conditions. Those skilled in the art have therefore long sought and will greatly appreciate the present invention which addresses these and other problems.
The present invention was designed to provide more efficient operation to thereby save time and reduce drilling costs, significantly improve speed of breaking pipe joints during a wet trip, permit increased automation to reduce required manpower, improve safety, and to reduce any possible well fluid loss into the environment.
Therefore, it is an object of the present invention to provide an improved wellbore fluid recovery system.
Another object of the present invention is to have the ability to reduce the time required for breaking joints during a wet trip.
Yet another object of the present invention is to reduce the size of the container positioned around the pipe joint to catch fluid when the joint is broken.
An advantage of the present invention is improved rig safety.
Another advantage of the present invention is faster operation.
Yet another advantage is lower costs.
These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims.
Therefore, the present invention provides for a wellbore fluid recovery system for recovering wellbore fluid when breaking one or more joints of wellbore tubulars comprising elements such as a container mountable around each of the one or more joints of the wellbore tubulars, a receiving tank, a first conduit between the container and the receiving tank, and a vacuum source operable for producing a vacuum within the receiving tank.
A first valve may preferably be provided for controlling flow through the first conduit. A vacuum tank is included in a preferred embodiment of the invention and the vacuum source may be adapted for producing a vacuum in the vacuum tank. A second conduit between the vacuum tank and the receiving tank is preferably provided with a second valve for controlling flow through the second conduit. A wellbore fluid storage tank, such as a trip tank, is connected to the receiving tank by a third conduit. A third valve controls flow through the third conduit.
In one preferred embodiment, the container for attachment around the pipe joint has a container volume less than a volume of the column of wellbore fluid to thereby provide a more compact container.
The method of the invention may preferably comprise steps such as the steps of placing the container around the joint, unscrewing the joint, applying the vacuum to the container, and collecting the fluid in the receiving tank. The step of applying the vacuum may further comprise opening the first valve to permit fluid communication between the receiving tank and the container. Prior to opening the first valve, the vacuum is preferably produced in the receiving tank. In a preferred embodiment, the vacuum is first produced in the vacuum tank and then the second valve between the vacuum tank and the receiving tank is opened. Prior to operation, all three valves are closed. After fluid is collected in the receiving tank, the third valve is opened to drain the wellbore fluid into a storage tank.